1. Field of the Invention
This invention relates to papermakers' fabrics.
2. Description of the Prior Art
There have heretofore been many requirements for papermakers' fabrics. The requirements may be roughly sorted into the following three groups:
Group I PA1 Group II PA1 Group III
Prevention of generation of wire marking, Sufficient tanglement of cellulosic fibers, and PA2 Problems as to the quality of paper or as to the retention of paper obtained; PA2 Improvement in wear resistance of fabrics and PA2 Extension of the service life thereof; and PA2 Satisfactory drainage, and the like.
The requirements in the respective Groups are associated with one another in many respects. Roughly speaking, the problems in Group I are greatly associated mainly with the structure of the papermaking side surface of the fabric, the problems in Group II are mostly associated with the structure of the running side surface (which is the reverse side surface or roller side surface) of the fabric, and the problems in Group III are associated with the entire fabric.
Such problems must be solved in the field not only of multi-layer fabrics but also single layer fabrics.
There have heretofore been proposed many approaches to the solution of the problems in Group I. However, no sufficient efforts have been made to improve the papermakers' fabrics in wear resistance except that the running side of the fabric is made to take a wefts-wearing form only to prevent the warps of the fabric from being worn.
On the other hand, there have recently been made many requirements such as the speed-up of papermaking, an increase in amounts of filler used and an increased necessity of manufacture of neutral paper, and, in addition, a serious problem has been raised as to the wear resistance of the papermaking fabrics.
FIG. 5 is a complete design showing a conventionally used papermakers' fabric consisting of 16 warps, 16 upper wefts and 16 lower wefts. In the Figure, the symbol "O" shows a position where the warp interlaces with the weft of the running side surface in the fabric, and the symbol "X" shows a position where the warp interlaces with the weft of the papermaking side surface. Accordingly, the distance between two adjacent "O" symbols indicates the length of one crimp of the weft in the running side surface. In the conventional papermakers' fabrics of FIG. 5, the adjacent two wefts in the running side surface are the same in length of crimp (or crimped portion).
In such conventional papermakers' fabrics, it has been attempted to use wefts having a large diameter in the running side surface to meet such requirements as the above, to improve the fabrics in wear resistance to some extent. In this case, however, the balance between the wefts and the warps is lost since the former are bigger in diameter than the latter, thus deteriorating the crimpiness and generating wire marking.
As will be understood from the problems in said Group III, a change in the structure of the running side surface will also affect the drainage, and the problems will not be solved by a mere makeshift measure such as the use of wefts having a bigger diameter.